1. Field of the Invention
The present invention relates to a display device and a manufacturing method thereof, and more particularly to a technique which is effectively applicable to a liquid crystal display device and a manufacturing method of the liquid crystal display device.
2. Description of Related Arts
Conventionally, as a display device, there has been known a liquid crystal display device which includes a liquid crystal display panel sealing liquid crystal between two substrates. Further, as a liquid crystal display device, there has been known a so-called active-matrix-type liquid crystal display device.
The active-matrix type liquid crystal display device includes the above-mentioned liquid crystal display panel, a plurality of scanning signal lines, a plurality of video signal lines, a plurality of active elements, a plurality of pixel electrodes, and a counter electrode, wherein the plurality of active elements and the plurality of pixel electrodes are arranged in a matrix array. In the active-matrix-type liquid crystal display device, in general, a TFT (thin film transistor) having the MIS structure (including MOS structure) is used as the active element.
Further, in the liquid crystal display panel, the scanning signal lines, the video signal lines, the TFTs and the pixel electrodes are formed on one substrate (TFT substrate) out of two substrates. Here, the pixel electrode is arranged in a region surrounded by two neighboring scanning signal lines and two neighboring video signal lines, and is connected to either one of a source or a drain of the TFT. Further, a gate of the TFT is connected to the scanning signal line, and either one of the source and the drain of the TFT to which the pixel electrode is not connected is connected to the video signal line.
Further, in the liquid crystal display panel, the pixel electrodes and the counter electrode are electrodes for driving the liquid crystal, wherein the counter electrode may be formed on the TFT substrate or may be formed on another substrate (counter substrate) out of the above-mentioned two substrates.
Here, on the TFT substrate, the pixel electrodes and two neighboring video signal lines arranged close to each other with the pixel electrode sandwiched therebetween are formed by way of an insulation layer, in general. Accordingly, a parasitic capacitance (also referred to as a line capacitance) is formed between the pixel electrode and two video signal lines.
In manufacturing the TFT substrate, the pixel electrode is formed such that a value of the parasitic capacitance formed between the pixel electrode and the video signal line arranged on a left side of the pixel electrode and a value of the parasitic capacitance formed between the pixel electrode and the video signal line arranged on a right side of the pixel electrode have the substantially same value. However, due to the displacement of positions where the video signal lines DL are formed, for example, there may be a case where the values of two parasitic capacitances differ from each other. When the values of two parasitic capacitances formed on the left and right sides of one pixel electrode differ from each other, for example, a potential of the pixel electrode is fluctuated thus giving rise to a phenomenon referred to as a longitudinal smear. Accordingly, in a conventional manufacturing method of a TFT substrate, for example, a thickness of an insulation layer interposed between the video signal line DL and the pixel electrode PX is increased up to a thickness which can prevent the fluctuation of the potential of the pixel electrode attributed to the difference between values of two parasitic capacitances formed on left and right sides of one pixel electrode.
Further, in the conventional liquid crystal display panel, as a method for suppressing a longitudinal smear, there has been proposed a method which forms a shielding electrode, for example. As such a method which forms the shielding electrode, there has been known a method which forms a shielding electrode overlapping a video signal line DL on the counter substrate (see patent document 1 (Japanese Patent Laid-open No. 2004-213031), for example) or a method which forms a shielding electrode between the video signal line and the pixel electrode on the TFT substrate (see patent document 2 (Japanese Patent Laid-open No. 2003-177414), for example).